Flow Contingency Factor

The Downstream Control Function rule editor offers a Rule Modifier that is not available to a Release Function rule— a Flow Contingency Factor. The purpose for this factor is to enable you to apply an uncertainty factor to the cumulative local flow so that the downstream control objective can still be met even when the quantity of the local flow is most uncertain.

If the limit type of the downstream control rule is Maximum, ResSim will use the contingency factor to increase the cumulative local flow at the control point which effectively reduces the available space at the control point. The reduced available space will cause the reservoir to release less than it would have without the contingency factor. This would make the operation appear more "conservative".

If the rule's limit type is Minimum, the contingency factor will be used to decrease the cumulative local flow, effectively increasing the available space at the control point and causing the reservoir to release more than it would have without the contingency factor, thus reducing the risk of not meeting the objective.

To apply a contingency to the cumulative local flows at the Downstream Location:

• Click the Flow Contingency button to open the Flow Contingency for Downstream Operation dialog ("Figure: Flow Contingency for Downstream Operation").
  
  

  Figure: Flow Contingency for Downstream Operation
• Two options are available for specifying the Flow Contingency factor:
  • Constant Contingency percentage — select this radio button if you want the local flow to be increased by a constant percentage, then enter a value in the textbox. For example, if you want to adjust the cumulative local flow by 20%, enter 20 in the textbox.
  • Contingency percentage as a function of Cumulative local flow — select this ratio button if you want the contingency factor to vary with the magnitude of flow. With this option, you must enter a relationship between the computed cumulative local flow at the control point and the contingency factor to be applied to it in the downstream control computations. For example, if the estimate of local flow is more uncertain under high flow conditions than under low, base flow conditions, you could enter a relationship where the contingency factor is zero or very small for smaller flow values and increases with larger flow values.

• Click OK to save your settings and close the Flow Contingency… editor.

If you specified a flow contingency factor or relationship, the Flow Contingency checkbox will be checked: in the Downstream Control Function rule editor.